<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        div{
            width: 500vw;
            height: 100vh;
            background-color: yellow;
        }
    </style>
</head>
<body>
    <!-- vh 和 vw -->
    <!-- vh (view-height)
              100vh === 视口的宽度
         vw (view-width)
              100vw === 视口的高度

        iphone6  100vw === 375px  1vw = 3.75px

        iphone6 plus  100vw === 414px 1vw = 4.14px

        html font-size  用js动态计算

        font-size:???vw
-->
    <div></div>
</body>
</html>